This invention relates generally to a control system for modulating electrically-operated expansion valves.
The type of refrigeration system where this invention would be applied would generally include a compressor, a condensor, an expansion device and an evaporator. The expansion device controls the flow of liquid refrigerant to the evaporator in response to a control system.
Efficient use of the evaporator surface in a refrigeration system requires that the expansion device provide liquid refrigerant to the evaporator in proportion to the requirement for cooling. To protect the compressor from "liquid slugging", excess flow of liquid must be avoided. To insure that liquid refrigerant does not leave the evaporator, the degrees above the boiling point temperature, generally called superheat, must be controlled. Heretofore, superheat has been controlled by approximation with a fixed restriction or by a mechanical valve powered by a temperature sensitive modulating diaphragm operator such as shown in U.S. Pat. No. 3,742,722, or by electrically operated expansion valves, both modulating and non-modulating in operation. U.S. Pat. No. 3,537,272 discloses a superheat control system for an electrically operated expansion valve for non-modulating operation.